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THE

TRANSIT OF VENUS

ITS MEANING AND USE

BY

T. H. BUDD, F.R.A.S.

LONDON

LONGMANS, GREEN, AND CO.

1875

All rights reserved

MUSEUM

PREFACE.

A QUESTION was asked in Punch not long ago, whether any one would explain the 'Transit of Venus.' It has occurred to the writer that an explanation in simple and untechnical language might indeed instruct as well as amuse those who are sufficiently curious to think about the matter, but who, perhaps, from want of time and leisure, cannot bring themselves to face the apparently overwhelming difficulties connected with the study of Astronomy in general, which they think they must overcome before they can arrive at the meaning of the (astronomically speaking) great event that occurred in December, 1874. Let me, however, assure my readers it can be made intelligible even to those who have never looked into a book on Astronomy. A perusal of the following pages will, I hope, prove my assertion.

THE

TRANSIT OF VENUS.

SECTION I.

FIRST of all, let me explain what the transit of Venus is. It is, in fact, the passing of the planet between the Earth and the Sun in such a way as that it will be actually seen from the Earth travelling across the Sun's face. Were Venus nearer the Earth, so as to appear as large as the Moon, the planet being in fact nearly three times as large in diameter as the Moon is, her transit across the Sun would cause an eclipse of the Sun. Being very much more distant from us, however, than the Moon is, and consequently appearing very much smaller, the eclipse' is reduced to a 'transit,' and, instead of covering the face of the Sun, the planet appears during the transit like a small round black spot. We all know that an eclipse of the Sun is caused by the Moon passing between the Sun and the Earth, they being all three in a line. In like manner, to cause a transit, the Sun, the planet,

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